16 September, 2013

From the Disappearance of Indian Vultures to Chinese Antibiotic Abuse

Indian vultures are famous for their efficient dietary behavior. These wild birds live on animal carcasses and are able to scavenge a dead cow in 20 minutes. But since 1995, vultures in India have suffered critical decline in number by more than 95%. Their weird disappearance once sent the sophisticated ecological system of south Asia into a vast chaos. How could Indian vultures encounter a surviving crisis like this?

Researches led by American microbiologist J. Lindsay Oaks a couple of years ago attributed their near extinction to a cheap and widely used veterinary drug called diclofenac sodium, an anti-inflammatory drug known to be toxic to the kidneys of mammals. Oaks' research team discovered that these vultures died of visceral gout and kidney failure while feeding on dead cattle or bodies of other livestock that have been treated with diclofenac.

India is one of the few countries of the world that has retained the religious tradition of celestial burial. Indian farmers historically left their dead cows (which is often considered as sacred) on an open ground for vultures to consume. It is not necessarily that the widespread of diclofenac may have caused the death of Indian cattle because the fatal dose of the drug on mammals is a lot larger than on fowls. Acute toxicity test of diclofenac (LD50 data) shows that when the substance builds up to 150 mg per kg in the body of mice, at least 50% of the test mice would die of diclofenac associated adverse effects. Pakistani avian pathologist Irtaza Hussain reports on his studies that an oral exposure to 10-20 mg/kg of the substance can lead to viscera gout and renal parenchymal disease in chicks and pigeons.

Though I'm still not sure what exact amount may lead to the death of the scavenging bird, one thing I'm certain of is the persistent and incredible abuse of anti-inflammatory drugs in India's animal husbandry. The same alarming case is with Chinese stock and poultry farming.

We are among the world's most dare-devil users of veterinary antibiotics and growth hormones. According to public statistics, about 210,000 tons antibiotic BPCs are produced annually in China, with at least 41 percent entering the sectors of breeding and food processing. Chinese consumption of antibiotics amounts to 138 grams per capita, 10 times of the US consumption. National food safety institutions also find out more than one thirds of the absorbed antibiotics come from meat product that are commonly seen as chicken, duck, fish and pork.

Usually, the excessive use of antibiotics can result in two adverse effects: drug resistance and drug residue problem. A more worrying consequence recently proposed by a Sino-US joint study on Chinese pig farms points out that the accumulated Antibiotic Resistance Genes (ARGs) found in livestock manure may have spread everywhere via mixed fertilizers, underground water and downstream river. The high mobility of ARGs means they can be easily transferred to other lethal germs or microbes that cause human diseases when the carried ARGs might disable all available human antibiotics. The co-authors of the study have hence named ARGs emerging contaminants posing a potential worldwide human health risk.

To save the reckless avian scavenger, Indian government has banned diclofenac for veterinary use in 2006, though the drug are still applied among ordinary peasants. Sad news for Chinese diners: legislative move to address antibiotic abuse has far from been put on agenda.